1. Field of the Invention
The invention belongs to the field of storage of fruits and specifically relates to an application of polyhexamethylene guanidine hydrochloride in the control of citrus sour rot and a citrus preservative.
2. Description of the Prior Art
Citrus is the first major fruit around the world, and is cultivated in 138 countries with the area of about 6.67 million hectares and the annual total output of more than one hundred million tons, wherein the annual total output accounts for 22% of the total output of fruits around the world. According to statistics, in 2008, the citrus cultivation area in China achieved 30.45 million mus, the total output was 23.31 million tons and accounted for about 23% of the citrus output around the world, and China was the largest citrus production country in the world. Guangdong province is one of the main citrus producing areas in China, and ‘Shatang’ mandarin are the most unique variety in the citrus varieties in Guangdong province and are very competitive in fruit markets at home and abroad. However, due to the unique biological characteristics, ‘Shatang’ mandarin are difficult to store in comparison with other citrus fruits, the post-harvest loss is quite serious, and the annular loss is above hundreds of million Chinese yuan (CHY), so that the development of the industry of ‘Shatang’ mandarin is seriously restricted.
Citrus belongs to a non-climacteric fruit, but the vigorous post-harvest respiratory metabolism can cause the rapid decline in nutrition and flavor quality. ‘Shatang’ mandarin fruit are characterized by thin in skin, juicy and vulnerable to post-harvest diseases, which make it difficult to store. The main post-harvest diseases for the fruit include sour rot, green and blue mold, black rot and blossom-end rot. At present, the most effective way to control the decay of ‘Shatang’ mandarin fruit is the application of low-temperature in combination with chemical bactericides. The bactericides include carbendazim, mildothane, imazalil, guazatine, and the like, but the way is still not very ideal to control the decay, in particular to the sour rot.
At present, the sour rot is one of the diseases which are most common and most difficult to control during storage and transportation of ‘Shatang’ mandarin fruit. The pathogenic fungi are Geotrichum candidum in Hyphomycetes, Deuteromycota, which infect the fruit through the damaged part. Geotrichum candidum only infects the fruit, generally mature or overripe fruits, and in particular to the fruit during the storage period. The incidence rate of sour rot is affected by preharvest cultivation measures, maturity, harvesting methods, fruit water status, storage and transportation measures and other factors. For example, the incidence rate of the sour rot in the main production area of ‘Shatang’ mandarin in Guangdong province in 2007 was below 10%, while the incidence rate at the beginning of 2010 was as high as above 50% due to the weather. Sour rot has not been controlled efficiently by imidazole and benzimidazole. Guazatine is effective to control sour rot in citrus fruit, but the use of guazatine was very limited due to pesticide residues and safety issue. Considering carcinogenic risk, Guazatine has been forbidden in USA Therefore, it is imperative to seek a safe, efficient and simple technology to control sour rot in citrus.
PHMG (polyhexamethylene guanidine hydrochloride, polyhexamethylene guanidine) is an environment-friendly broad-spectrum antibacterial agent newly synthesized internationally. PHMG belongs to guanidine derivatives and is a cationic polymer. PHMG can efficiently kill bacteria by attacking the cellular wall and cytoplasma membrane systems. PHMG can rapidly break through cytoplasma membranes when it combine with the fatty acids in phospholipid of cell membrane, breach nuclei of cells of the pathogenic bacteria, enable cell inclusion of the pathogenic bacteria to outflow. PHMG is a polymer and less prone to being absorbed by animal, so that its toxicity can be greatly reduced. According to the results of Russian quarantine departments, the half lethal dose (LD50) of PHMG to mice is 25,000 mg/kg, so that PHMG is at actually non-toxic level. As PHMG has the characteristics of no toxicity, high efficiency, stability and the like, PHMG can be widely applied to hospital sterilization and sterilization of drinking water and food processing equipments. PHMG has strong effects of killing and inhibiting bacteria and viruses, and the studies and the applications in the effect of inhibiting fungi are fewer. At present, there have been no reports about the application and studies of PHMG in the control of post-harvest fruit and vegetable fungal disease.